Image sensors are widely used in digital still cameras, cellular phones, security cameras, medical devices, and automobiles. As the applications for image sensors increases, demand increases for image sensors with increased image quality and improved performance. Complementary metal-oxide-semiconductor (“CMOS”) technology is used to manufacture lower cost image sensors on silicon substrates. Some CMOS image sensors are designed for capturing high dynamic range (“HDR”) images.
The size of image sensors is also shrinking, even as consumers desire increasing performance and functionality. Therefore, designers must balance adding features to image sensor with the overall size of the image sensor. To add HDR capability to image sensors, some designers have used two photodiodes in a combination pixel to capture two different images at different light levels. One sub-pixel in a combination pixel can be used to sense bright light conditions while another sub-pixel in the combination pixel can be used to sense low light conditions. However, using two photodiodes has a large impact on available semiconductor real estate. Some image sensors generate HDR images by capturing consecutive images. However, readout time between capturing the consecutive images impacts the final HDR image, especially when a scene includes moving subjects. Other contexts, such as gesture recognition also place a premium on capturing consecutive images in short time periods.